Figure 3.

Images of a Platinum surface taken all at a scan frequency of 1 line/s, but at different
settings for the feedback loop. From left to right, feedback parameters settings are (in arbitrary units): 90/45,
45/22.5, 15/7.5, 5/2.5 and 1/0.5. The images and graphs in the same column correspond
to a common data set, since the corresponding images have been acquired simultaneously
at a fixed values of the feedback loop. The upper row shows topographic images, the
middle row amplitude images and the lower row graphs of the PSD curves of surface
roughness. In each graph, the PSD of surface roughness has been calculated for the
topography and amplitude image shown in the corresponding column, as well as for the
difference ztrue = zfb - ΔIerr (corresponding image not shown). Lateral size of the larger images is 10 μm, smaller images show a zoom of 1 μm. The total grey scale of all images is 5 nm (large and small scale images as well
as topographic and amplitude images). Lower row: PSD curves calculated from the topography
and amplitude images as well as the difference data (image not shown). The grid lines
for the PSD graphs are Δlog[κ] = 1 (horizontal axis) and Δlog[PSD] = 1 (vertical axis). Green lines correspond
to the PSD curves of topography plus error signal, blue curves to the topography and
red curves to the error signal.